Don't add it to an existing long list of limericks
The nodes limerick and limericks are both currently overflowing with limericks of varying quality. These limericks have only one thing in common, which is their rhyming scheme. If all contributions in the limerick form were to be added to a single node, the resulting list would be unworkably long, but even if this were feasible, it is utterly undesirable. Imagine, if you will, that all of the song lyrics on E2 were appended to a single node called song lyrics, or every daylog were moved to daylogs.

Create it as a separate node
The resulting node will be quite short, which may not please everybody, but the worthiness of your noding will be judged by the quality of the limerick. If your node attracts downvotes, this means the E2 community does not feel that the poem was really worthy of inclusion. If the limerick is particularly good, or original, it will attract positive votes, and your creation of a new node will not have been for nothing.